Ethernet automatic media selection logic with preferred medium selector

ABSTRACT

A physical layer device comprises an interface that communicates with a media access control (MAC) device. A first circuit attempts to establish a first link using a first transceiver over a first medium. A second circuit attempts to establish a second link using a second transceiver over a second medium that is different than the first medium. A media selector communicates with the interface and the first and second circuits and that enables data flow from the first medium to the MAC device using the interface when the first link is established first. A preferred medium selector communicates with the media selector and is configurable in one of a plurality of medium preference states.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent Ser. No. 10/435,301,filed May 9, 2003, which application claims the benefit of U.S.Provisional Application No. 60/438,933, filed on Jan. 9, 2003, and U.S.patent application Ser. No. 09/991,046, filed Nov. 21, 2001, all ofwhich are incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to computer networks, and moreparticularly to an automatic media selector for Ethernet networks.

BACKGROUND OF THE INVENTION

Referring now to FIG. 1, a data link layer 10 of the open systemsinterconnection (OSI) model includes a logical link control (LLC) layer12 and a media access control (MAC) layer 14. The LLC layer 12 addressesand exchanges data with a network layer 16. The MAC layer 14 provides aninterface between the LLC layer 12 and a physical layer device 18. TheMAC layer 14 frames data for transmission over the network and thenpasses the frame to the physical layer device 18 for transmission as astream of bits. In other words, the MAC layer 14 frames data intodistinct units or packets that are transmitted one at a time over thenetwork.

The physical layer device 18 typically includes a physical codingsublayer (PCS) 20, a physical medium attachment (PMA) sublayer 22, andan autonegotiation sublayer 24. A medium dependent interface (MDI) 26such as an RJ-45 connector connects the physical layer device 18 tomedia 28 such as twisted pair wires, optical fiber or other media. TheIEEE 802.3 specification, which is hereby incorporated by reference,further defines how physical network interfaces operate with differenttypes of media such as coaxial cable, twisted-pair cable and opticalfiber.

To improve flexibility, the physical layer device 18 of some networkdevices has been designed to be connected to different types of media.The manufacturer and/or the user may not know the type of media thatwill be used at the time of manufacturing or purchase. The type of mediathat is used may also change over time.

For example, the physical layer device 18 is selectively connectable tocopper or optical fiber. Currently, the PCS sublayer 20 of the physicallayer device 18 is programmed to handle the specific type of media thatwill be used. For example when optical fiber is used, the operating modeof the PCS 20 is programmed to provide an optical interface. If the userlater decides to use a different type of media such as copper, theoperating mode of the PCS 20 is programmed to provide a copperinterface. The reprogramming process increases the cost of operating thenetwork.

The autonegotiation sublayer 24 initiates the exchange of informationbetween two connected network devices and automatically configures thedevices to take maximum advantage of their respective abilities. Theautonegotiation sublayer 24 advertises the abilities of the networkdevice, acknowledges receipt, identifies common modes of operation, andrejects the use of operational modes that are not shared or supported byboth devices. When more than one common mode of operation exists betweenthe devices, an arbitration function of the autonegotiation layer 24identifies and selects a single mode of operation. After autonegotiationis complete, the devices establish a link and exchange data.

SUMMARY OF THE INVENTION

A network device includes a media access controller (MAC) and a physicallayer device including an interface that communicates with the MAC,first and second transceivers, and a first autonegotiation circuit thatattempts to establish a first link using the first transceiver over afirst medium. A second autonegotiation circuit attempts to establish asecond link using the second transceiver over a second medium. A mediaselector communicates with the interface and the first and secondautonegotiation circuits and enables data flow from the first medium tothe MAC using the interface when the link over the first medium isestablished first. A preferred medium selector communicates with themedia selector and has a no preference state and at least one of firstmedium preference state and a second medium preference state.

In other features, when the preferred medium selector has the secondmedium preference state, the media selector monitors the second mediumfor a qualified energy detect event. When the qualified energy detectevent occurs, the media selector blocks a link status of the firstmedium and starts a break link timer. If a link is established by thesecond medium before the break link timer is up, the first link over thefirst medium is brought down. If a link is not established by the secondmedium before the break link timer is up, the first link over the firstmedium is not brought down.

In still other features, the first medium is copper and the secondmedium is fiber. The qualified energy detect event occurs when the fiberis active during a plurality of consecutive windows.

In yet other features, the first medium is fiber and the second mediumis copper. The qualified energy detect event occurs when the copper isactive during a plurality of consecutive windows.

In still other features, the media selector powers down at least one ofthe second autonegotiation circuit and the second transceiver when thefirst link over the first medium is established first. The mediaselector powers up the second autonegotiation circuit and/or the secondtransceiver when the first link is lost. The media selector enables dataflow from the second medium to the MAC using the interface when thesecond link over the second medium is established first. The mediaselector powers down at least one of the first autonegotiation circuitand the first transceiver when the second link over the second medium isestablished first. The media selector powers up the at least one of thefirst autonegotiation circuit and the first transceiver when the secondlink is lost.

In still other features, the interface is a physical coding sublayer(PCS) circuit. A status indicator identifies a current active link.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a partial OSI network model for communication between networkdevices according to the prior art;

FIG. 2 is a functional block diagram of a network device including amedia access control (MAC) layer and a physical layer device with anautomatic media selector according to the present invention;

FIG. 3 is a more detailed functional block diagram of a first exemplaryphysical layer device including the automatic media selector of FIG. 2;

FIG. 4 is a more detailed functional block diagram of a second exemplaryphysical layer device including the automatic media selector of FIG. 2;

FIG. 5 illustrates steps performed by the automatic media selector ofFIGS. 3 and 4;

FIG. 6 is a more detailed functional block diagram of a third exemplaryphysical layer device including the automatic media selector and apreferred medium selector;

FIG. 7 is a more detailed functional block diagram of a fourth exemplaryphysical layer device including the automatic media selector and apreferred medium selector;

FIG. 8 illustrates steps performed by the alternate automatic mediaselectors of FIGS. 6 and 7 with the preferred medium selector accordingto the present invention;

FIG. 9 illustrates steps performed by the alternate automatic mediaselector with the preferred medium selector to detect copper activitythat is sufficient to break a fiber link when copper is preferred; and

FIG. 10 illustrates steps performed by the alternate automatic mediaselector of FIG. 8 with the preferred medium selector to detect fiberactivity that is sufficient to break a copper link when fiber ispreferred.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiment(s) is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses. For purposes of clarity, the same referencenumbers will be used in the drawings to identify similar elements.

Referring now to FIG. 2, a media access control (MAC) layer 50communicates with a physical layer device 52 of a network device. Thephysical layer device 52 includes analog and digital circuits 54 and 56.In the exemplary embodiment, the analog circuits 54 are physicallyconnected to copper media 60 and/or fiber media 64 using media dependentinterfaces (MDI) (not shown in FIG. 2) such as an RJ-45 connector or afiber connector. Skilled artisans can appreciate that the presentinvention applies to other types of media such as radio frequency aswell.

In use, the digital circuits 56 of the physical layer device 52 includea physical coding sublayer (PCS) interface. Both the copper and fiberautonegotiation sublayers attempt to initiate a link over the copper andfiber media 60 and 64, respectively. If autonegotiation is completedover the fiber media, the PCS interface is configured for fiber. Thecopper autonegotiation sublayer and the copper transceiver arepreferably powered down. Data flow from the fiber media 64 to the MAClayer 50 is enabled. When the link over the fiber media 64 goes down,the copper autonegotiation layer and/or the copper transceiver arepowered back up.

Alternately, if autonegotiation and a link are completed over the coppermedia before or at the same time as the fiber media, the PCS interfaceis configured for copper. The fiber autonegotiation sublayer and thefiber transceiver are preferably powered down. Data flow from the coppermedia 60 to the MAC layer 50 is enabled. When the link over the coppermedia 60 goes down, the fiber autonegotiation sublayer and the fibertransceiver are powered up. As a result, the physical layer device 52automatically configures itself without requiring the physical layerdevice 52 (and/or the PCS thereof) to be reprogrammed.

Skilled artisans can appreciate that a standard interface may beprovided between the MAC layer 50 and the physical layer device 52. Forexample, the standard interface can be TBI, GMII, SGMI, RGMII, RTBI,MIl, RMII, SMII or other suitable interfaces.

Referring now to FIG. 3, the analog circuits 54 of a first exemplaryphysical layer device 52-1 are shown in further detail and include acopper transceiver 70 and a fiber transceiver 72. The digital circuits56 of the physical layer device 52-1 are also shown in further detailand include a copper autonegotiation circuit 76 and a fiberautonegotiation/link circuit 78 that are connected to the coppertransceiver 70 and fiber transceiver 72, respectively. A physical codingsublayer (PCS) interface 90 communicates with the copper transceiver 70,the copper autonegotiation circuit 76, the fiber autonegotiation/linkcircuit 78 and/or the fiber transceiver 72. The PCS interface 90 hasfirst and second modes of operation for copper and optical fiber,respectively, that can be selected by an automatic media selector 110 aswill be described more fully below.

During copper autonegotiation, the copper transceiver 70 transmits FastLink Pulse (FLP) bursts over the copper 60. The FLP pulse bursts containconfiguration parameters that the first network device wishes toadvertise. If the copper transceiver 70 receives FLP bursts, negotiationof the configuration parameters occurs and a link over the copper 60 isestablished and data is exchanged.

During fiber autonegotiation, code groups are initially transmitted bythe fiber transceiver 72. For example code groups such as KDKD . . . aretransmitted where each symbol represents multiple bits. Whenautonegotiation occurs, code groups such as KDCCKDCC . . . aretransmitted. The fiber autonegotiation/link circuit 78 monitors the codegroups and identifies sync status. When autonegotiation completes, alink over fiber 64 is established and data is exchanged.

The media selector 110 communicates with the copper autonegotiationcircuit 76, the fiber autonegotiation/link circuit 78, and/or the PCSinterface 90. The media selector 110 monitors the status of the copperautonegotiation circuit 76 and the fiber autonegotiation/link circuit 78to identify the media that establishes a link first. Once the link isestablished over one media, the autonegotiation circuit and/or thetransceiver associated with the other media are powered down until thelink goes down. When this occurs, the autonegotiation circuit and/or thetransceiver that is associated with the other media is powered back up.

Referring now to FIG. 4, reference numbers from FIG. 3 are used in FIG.4 where appropriate to identify the same elements. A second exemplaryphysical layer device 52-2 is shown. The PCS interface 90 may include acopper interface 114 and an optical fiber interface 116. As describedabove, the automatic media selector 110 selects one of the interfaces114 and 116 depending upon which media completes a link first. The otherinterface is preferably disabled and/or powered down until the link goesdown. Otherwise, the operation for the physical layer device 52-2 issimilar to the physical layer device 52-1.

Referring now to FIG. 5, steps for performing automatic media selectionaccording to the present invention are shown generally at 150. Controlbegins with step 152 and proceeds to step 154. In step 154, both copperand fiber autonegotiation are initiated. In step 156, the media selector110 determines whether a fiber link has completed. If the fiber link hascompleted, the media selector 110 powers down the copper interface 114,the copper autonegotiation circuit 76 and/or the copper transceiver 70in step 160. In step 162, the media selector 110 enables data flow overfiber to the MAC layer 50. In step 164, the media selector 110determines whether the fiber link is down. If not, control loops back tostep 164. Otherwise, control continues with step 168 where the circuitsthat were powered down in step 160 are powered back up. Controlcontinues from step 168 back to step 154.

If the fiber link does not complete first as determined in step 156,control continues with step 172. In step 172, control determines whethera copper link is established. If the copper link occurs, the mediaselector 110 powers down the fiber PCS interface 116, the fiberautonegotiation/link circuit 78 and/or the fiber transceiver 72 in step174. In step 176, the media selector 110 enables data flow over copperto the MAC layer 50. In step 178, the media selector 110 determineswhether the copper link is down. If not, control loops back to step 178.Otherwise, control continues with step 180 where the circuits that werepowered down in step 174 are powered back up. Control continues fromstep 180 to step 154.

The copper interface is employed as a default when both copper and fibercomplete the link at the same time. Alternatively, skilled artisans canappreciate that fiber can be selected as a default when both copper andfiber complete the link at the same time. However, both copper and fiberwill rarely complete the link at the same time. As can be appreciated,the physical layer device can be implemented in a variety of ways suchas analog and/or digital circuits, software executed by a processor andmemory, application specific integrated circuits, or in any othersuitable manner.

Referring now to FIGS. 6 and 7, a preferred medium selector 190 is addedto the devices in FIGS. 3 and 4. The preferred medium selector 190allows a user to select a preferred medium, such as copper or fiber oran unlinked medium, or to not select a preferred medium. If a preferredmedium is not selected, the devices in FIGS. 6 and 7 operate the same asthose shown in FIGS. 3 and 4 and described above. If a preferred mediumis selected and a link is established on the non-preferred medium first,the devices in FIGS. 6 and 7 monitor for a qualified energy detect eventon the preferred medium. If a qualified energy detect event occurs, thenon-preferred link status is blocked for a predetermined period to allowthe preferred medium an opportunity to establish a link. Additionaldetails are set forth below.

Referring now to FIG. 8, steps performed by an alternate automatic mediaselector of FIGS. 6 and 7 with a preferred medium selector 190 accordingto the present invention are shown generally at 200. The automatic mediaselector with the preferred medium selector 190 allows a user to selectfiber or copper as a preferred media, no preferred medium (in which casecontrol will proceed as shown in FIG. 5) or an optional unlinked mediumstate (which will be described below).

For purposes of clarity, the steps in FIG. 8 that are the same as thosedepicted in FIG. 5 are labeled with the same reference numbers. When thecopper link is completed first, control continues from step 176 to step208 where control determines whether fiber is the preferred medium. Iffiber is not the preferred medium, control continues with step 210 wherecontrol determines whether the copper link is down. If the copper linkis not down, control continues with step 208. If the copper link is downin step 210, control continues with step 180 as described above.

If fiber is preferred in step 208, control determines whether there is aqualified fiber energy detect event in step 212 as will be describedbelow in conjunction with FIG. 10. If not, control continues with step210. If there is a qualified energy detect event as determined in step212, control starts a break link timer in step 216. For example, thebreak link timer can be set equal to 4 seconds, although longer orshorter periods may be used. In step 220, control blocks a link statussignal from the copper medium. In step 224, control determines whetherthe fiber link is up. If true, control continues with step 160. Iffalse, control determines whether the break link timer is up in step226. If false, control continues with step 220. Otherwise, controlcontinues with step 210.

When the fiber link completes first, control continues from step 162 tostep 230 where control determines whether copper is the preferredmedium. If false, control continues with step 232 where controldetermines whether the fiber link is down. If the fiber link is notdown, control continues with step 230. If the fiber link is down,control continues with step 168 as described above.

If copper is the preferred medium in step 230, control continues withstep 234 and determines whether there is a qualified copper energydetect event as described below in conjunction with FIG. 9. If false,control continues with step 232. If there is a qualified copper energydetect event, control starts a break link timer in step 236. Forexample, the break link timer can be set to 4 seconds, although shorteror longer periods may be used. The break link timers 216 and 236 canalso have different periods if desired. In step 240, control blocks alink status signal from the fiber medium. In step 244, controldetermines whether the copper link is up. If the copper link is up,control continues with step 174. If the copper link is not up in step244, control determines whether the break link timer is up in step 248.If true, control continues with step 232. If the break link timer is notup in step 248, control continues with step 240.

Before breaking an established link for the preferred medium, thepresent invention detects activity and then qualifies the detectedactivity to prevent noise from causing a switchover. On the copper side,wire activity on both pairs is monitored. Both pairs are preferablymonitored and OR-ed because the link partner may be attempting toperform auto-crossover. In a preferred embodiment, copper activity isacknowledged when there is activity during a window having apredetermined duration. For example, copper activity should occur onceevery 24 ms. Therefore a window that is longer than 24 ms is sufficient.For example, a window having a duration of 50 ms is suitable, althoughother longer or shorter periods will work. To qualify the copper energydetect, a plurality of consecutive windows should have activity. Forexample, 20 windows having a duration of 50 ms should have activity. Ascan be appreciated, other window durations and numbers of windows can berequired.

On the fiber side, a signal detect input of the fiber transceiver ismonitored. In a preferred embodiment, fiber activity is acknowledgedwhen there is activity during a window having a predetermined duration.For example, fiber activity should occur almost continuously. Therefore,the duration of a window is somewhat arbitrary. For example, a windowhaving a duration of 1 μs is suitable, although longer or shorterperiods will work. To qualify the fiber energy detect, a plurality ofconsecutive windows should have activity. For example, all of thewindows during a 1 second period should have activity. As can beappreciated, other window durations and numbers of windows can be used.In addition, if the signal detect signal is not available, any othersignal that relates to received fiber data can be used.

Referring now to FIG. 9, steps that are performed to detect qualifiedcopper activity that is sufficient to break a fiber link (when copper ispreferred) are shown at 300. Control enters in step 301 when step 234 inFIG. 8 is executed. In step 302, control sets copper activity (CA)=0. Instep 306, control supplies power to the 10BASET receiver. Alternately,the 10BASET receiver can be powered earlier. In step 310, control startstimer T1. In step 312, control sets counter1=1. In step 320, controlresets timer T2. In step 324, control samples wire activity on both ofthe pairs. If there is no wire activity on either pair, controlcontinues with step 332 and determines whether T2 is up. If T2 is notup, control loops back to step 328. If T2 is up, control determineswhether counter1=M in step 334. If step 334 is false, control incrementscounter1 in step 336 and loops back to step 320.

If there is wire activity on either pair during T2 as determined in step328, control increments CA in step 338. In step 340, control determineswhether T2 is up. If not control loops back to step 340. Otherwisecontrol continues with step 334. If the Counter1=M in step 334 andCA< >M in step 342, control sets a copper energy detect=false in step344 and control returns in step 348. If CA=M in step 342, control setscopper energy detect=true in step 350 and control returns in step 348.

Referring now to FIG. 10, steps that are performed to detect qualifiedfiber activity that is sufficient to break a copper link (when fiber ispreferred) are shown at 400. Control enters in step 401 after step 212is executed. In step 402, control sets fiber activity (FA)=0. In step406, control turns on a fiber activity or signal detector. Alternately,the fiber activity detector can be turned on earlier. In step 410,control starts timer T3. In step 412, control determines whether T3 isup. In step 416, control sets counter2=1. In step 420, control resetstimer T4. In step 424, control samples activity on the fiber. If thereis no activity on the fiber, control continues with step 432 anddetermines whether T4 is up. If not, control loops back to step 428. IfT4 is up, control determines whether counter2=P in step 434. If step 434is false, control increments a Counter2 in step 436 and loops back tostep 420.

If there is activity on the fiber during T4 as determined in step 428,control increments FA in step 438. In step 440, control determineswhether T4 is up. If not control loops back to step 440. Otherwisecontrol continues with step 434. If the Counter2=P in step 434 andFA< >P in step 442, control sets a fiber energy detect=false in step 444and control returns in step 448. If FA=P in step 442, control sets fiberenergy detect=true in step 450 and control returns in step 448.

While FIGS. 9 and 10 show one suitable way for counting and/or measuringwhether qualified fiber and copper activity is present on thenon-preferred medium, skilled artisans will appreciate that there areadditional ways to detect whether activity is present and/or qualified.These other algorithms in FIG. 3 should have the ability to detectactivity and be able to differentiate the activity from noise as opposedto other desired activity.

In addition, the preferred medium selector 190 may have an alternatemode of operation. The preferred medium selector 190 optionally allowsthe selection of the unlinked medium as the preferred medium. Whenactivity is sensed on the unlinked medium, the chip initiates the stepsthat are set forth above. For example, the preferred medium selector isset to the unlinked medium. In this example, the link over the coppermedium is established. While the copper link is active, the fibermedium, which is the unlinked medium, has activity. The preferred mediumselector acts as if the fiber medium is the preferred medium and followsthe steps set forth above.

Continuing with the same example, some time later, neither medium has anestablished link. Later, a link over the fiber medium is established.While the fiber link is active, the copper medium, which is the unlinkedmedium, has activity. The preferred medium selector acts as if thecopper medium is the preferred medium and follows the steps set forthabove. In FIG. 9, step 208 can be modified to determine whether fiber ispreferred or whether the unlinked medium is preferred. Likewise step 230can be modified to determine whether copper is preferred or whether theunlinked medium is preferred.

Thus it will be appreciated from the above, the present inventiondiscloses an automatic media selector, a method for selecting the media,and a method for selecting a preferred medium for Ethernet transceivers.It will be equally apparent and is contemplated that modification and/orchanges may be made in the illustrated embodiment without departure fromthe invention. Accordingly, it is expressly intended that the foregoingdescription and accompanying drawings are illustrative of preferredembodiments only, not limiting, and that the true spirit and scope ofthe present invention will be determined by reference to the appendedclaims and their legal equivalent.

1. A physical layer device, comprising: an interface that communicateswith a media access control (MAC) device; first and second transceivers;a first circuit that attempts to establish a first link using said firsttransceiver over a first medium; a second circuit that attempts toestablish a second link using said second transceiver over a secondmedium that is different than said first medium; a media selector thatcommunicates with said interface and said first and second circuits andthat enables data flow from said first medium to the MAC device usingsaid interface when said first link is established first; and apreferred medium selector that communicates with said media selector andthat is configurable in one of a plurality of medium preference states.2. The physical layer device of claim 1 wherein when said preferredmedium selector is in a first one of said plurality of medium preferencestates, said media selector monitors said second medium for a qualifiedenergy detect event.
 3. The physical layer device of claim 2 whereinwhen said qualified energy detect event occurs, said media selectorblocks a link status of said first medium.
 4. The physical layer deviceof claim 3 wherein when said qualified energy detect event occurs, saidmedia selector starts a break link timer.
 5. The physical layer deviceof claim 4 wherein if the second link is established by said secondmedium before said break link timer is up, said first link is broughtdown.
 6. The physical layer device of claim 4 wherein if the second linkis not established by said second medium before said break link timer isup, said first link is maintained.
 7. The physical layer device of claim2 wherein said first medium is copper and said second medium is fiber,and wherein said qualified energy detect event occurs when said fiber isactive during a plurality of consecutive windows.
 8. The physical layerdevice of claim 2 wherein said first medium is fiber and said secondmedium is copper, and wherein said qualified energy detect event occurswhen said copper is active during a plurality of consecutive windows. 9.The physical layer device of claim 1 wherein said media selector powersdown at least one of said second circuit and said second transceiverwhen said first link is established first.
 10. The physical layer deviceof claim 9 wherein said media selector powers up said at least one ofsaid second circuit and said second transceiver when said first link islost.
 11. The physical layer device of claim 1 wherein said mediaselector enables data flow from said second medium to the MAC deviceusing said interface when said second link over said second medium isestablished first.
 12. The physical layer device of claim 11 whereinsaid media selector powers down at least one of said first circuit andsaid first transceiver when said second link over said second medium isestablished first.
 13. The physical layer device of claim 12 whereinsaid media selector powers up said at least one of said first circuitand said first transceiver when said second link is lost.
 14. Thephysical layer device of claim 1 wherein said interface includes aphysical coding sublayer (PCS) circuit.
 15. The physical layer device ofclaim 1 further comprising a status indicator that identifies a currentactive link.
 16. The physical layer device of claim 1 wherein when saidpreferred medium selector is in a second one of said plurality of mediumpreference states, said media selector monitors an unlinked medium for aqualified energy detect event.
 17. The physical layer device of claim 16wherein when said qualified energy detect event occurs, said mediaselector blocks a link status of said first medium.
 18. The physicallayer device of claim 16 wherein when said qualified energy detect eventoccurs, said media selector starts a break link timer.
 19. The physicallayer device of claim 18 wherein if a link is established by saidpreviously unlinked medium before said break link timer is up, saidfirst link is brought down.
 20. The physical layer device of claim 18wherein if a link is not established by said unlinked medium before saidbreak link timer is up, said first link is maintained.
 21. A methodcomprising: providing an interface that communicates with a media accesscontrol (MAC) device; attempting to establish a first link using a firsttransceiver over a first medium; attempting to establish a second linkusing a second transceiver over a second medium that is different thansaid first medium; enabling data flow from said first medium to the MACdevice using said interface when said first link is established first;and selecting one of a plurality of medium preference states.
 22. Themethod of claim 21 further comprising monitoring said second medium fora qualified energy detect event when a first one of said plurality ofmedium preference states is selected.
 23. The method of claim 22 furthercomprising blocking a link status of said first medium when saidqualified energy detect event occurs.
 24. The method of claim 23 furthercomprising starting a break link timer when said qualified energy detectevent occurs.
 25. The method of claim 24 further comprising bringingsaid first link down when the second link is established by said secondmedium before said break link timer is up.
 26. The method of claim 24further comprising maintaining said first link when the second link isnot established by said second medium before said break link timer isup.
 27. The method of claim 22 wherein said first medium is copper andsaid second medium is fiber, and wherein said qualified energy detectevent occurs when said fiber is active during a plurality of consecutivewindows.
 28. The method of claim 22 wherein said first medium is fiberand said second medium is copper, and wherein said qualified energydetect event occurs when said copper is active during a plurality ofconsecutive windows.
 29. The method of claim 21 further comprisingpowering down said second transceiver when said first link isestablished first.
 30. The method of claim 29 further comprisingpowering up said second transceiver when said first link is lost. 31.The method of claim 21 further comprising enabling data flow from saidsecond medium to the MAC device using said interface when said secondlink over said second medium is established first.
 32. The method ofclaim 31 further comprising powering down said first transceiver whensaid second link over said second medium is established first.
 33. Themethod of claim 32 further comprising powering up said said firsttransceiver when said second link is lost.
 34. The method of claim 21wherein said interface includes a physical coding sublayer (PCS)circuit.
 35. The method of claim 21 further comprising a statusindicator that identifies a current active link.
 36. The method of claim21 further comprising monitoring an unlinked medium for a qualifiedenergy detect event when in a second one of said plurality of mediumpreference states.
 37. The method of claim 36 further comprisingblocking a link status of said first medium when said qualified energydetect event occurs.
 38. The method of claim 36 further comprisingstarting a break link timer when said qualified energy detect eventoccurs.
 39. The method of claim 38 further comprising bringing saidfirst link down when a link is established by said previously unlinkedmedium before said break link timer is up.
 40. The method of claim 38further comprising maintaining said first link when a link is notestablished by said unlinked medium before said break link timer is up.41. A physical layer device, comprising: an interface that communicateswith a media access control (MAC) device; first and second transceivers;a first circuit that attempts to establish a first link using said firsttransceiver over a first medium; a second circuit that attempts toestablish a second link using said second transceiver over a secondmedium that is different than said first medium; and a media selectorthat communicates with said interface and said first and second circuitsand that enables data flow from said first medium to the MAC deviceusing said interface when said first link is established first, and thatmonitors said second medium for a qualified energy detect event duringsaid first link.
 42. The physical layer device of claim 41 wherein whensaid qualified energy detect event occurs, said media selector blocks alink status of said first medium.
 43. The physical layer device of claim42 wherein when said qualified energy detect event occurs, said mediaselector starts a break link timer.
 44. The physical layer device ofclaim 43 wherein if the second link is established by said second mediumbefore said break link timer is up, said first link is brought down. 45.The physical layer device of claim 43 wherein if the second link is notestablished by said second medium before said break link timer is up,said first link is maintained.
 46. The physical layer device of claim 41wherein said first medium is copper and said second medium is fiber, andwherein said qualified energy detect event occurs when said fiber isactive during a plurality of consecutive windows.
 47. The physical layerdevice of claim 41 wherein said first medium is fiber and said secondmedium is copper, and wherein said qualified energy detect event occurswhen said copper is active during a plurality of consecutive windows.48. The physical layer device of claim 41 wherein said media selectorpowers down said second transceiver when said first link is establishedfirst and powers up said second transceiver when said first link islost.
 49. The physical layer device of claim 41 wherein said mediaselector enables data flow from said second medium to the MAC deviceusing said interface when said second link over said second medium isestablished first, powers down said first transceiver when said secondlink over said second medium is established first, and powers up saidfirst transceiver when said second link is lost.
 50. The physical layerdevice of claim 41 wherein said interface includes a physical codingsublayer (PCS) circuit.
 51. A method comprising: providing an interfacethat communicates with a media access control (MAC) device; attemptingto establish a first link using a first transceiver over a first medium;attempting to establish a second link using a second transceiver over asecond medium that is different than said first medium; enabling dataflow from said first medium to the MAC device using said interface whensaid first link is established first; and monitoring said second mediumfor a qualified energy detect event during said first link.
 52. Themethod of claim 51 further comprising blocking a link status of saidfirst medium when said qualified energy detect event occurs.
 53. Themethod of claim 52 further comprising starting a break link timer whensaid qualified energy detect event occurs.
 54. The method of claim 53further comprising bringing down said first link when the second link isestablished by said second medium before said break link timer is up.55. The method of claim 53 further comprising maintaining said firstlink when the second link is not established by said second mediumbefore said break link timer is up.
 56. The method of claim 51 whereinsaid first medium is copper and said second medium is fiber, and whereinsaid qualified energy detect event occurs when said fiber is activeduring a plurality of consecutive windows.
 57. The method of claim 51wherein said first medium is fiber and said second medium is copper, andwherein said qualified energy detect event occurs when said copper isactive during a plurality of consecutive windows.
 58. The method ofclaim 51 further comprising: powering down said second transceiver whensaid first link is established first; and powering up said at least oneof said second circuit and said second transceiver when said first linkis lost.
 59. The method of claim 51 further comprising: enabling dataflow from said second medium to the MAC device using said interface whensaid second link over said second medium is established first; poweringdown said first transceiver when said second link over said secondmedium is established first; and powering up said first transceiver whensaid second link is lost.
 60. The method of claim 51 wherein saidinterface includes a physical coding sublayer (PCS) circuit.